Crystalline multilayer oxide thin films structure in semiconductor device

ABSTRACT

Provided is a highly conductive crystalline multilayer structure including a corundum-structured crystalline oxide thin film whose resistance has not increased even after annealing (heating). The crystalline multilayer structure includes a base substrate and the corundum-structured crystalline oxide thin film disposed directly on the base substrate or with another layer therebetween. The crystalline oxide thin film is 1 μm or more in a thickness and 80 mΩcm or less in an electrical resistivity. A semiconductor device includes the crystalline multilayer structure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent Ser. No. 16/014,633,filed Jun. 21, 2018, which is a continuation of U.S. patent Ser. No.14/577,917, filed Dec. 19, 2014 (now U.S. patent Ser. No. 10/109,707),which claims priority from Japanese Patent Application No. 2014-072779,filed Mar. 31, 2014, all of which applications are expresslyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a crystalline multilayer structure anda semiconductor device.

BACKGROUND ART

Known methods for forming a gallium oxide-based thin film having highcrystallinity on a sample to be deposited include a film forming methodusing water fine particles, such as the mist CVD method (PatentLiterature 1: Japanese Unexamined Patent Application Publication No.2013-28480). For example, this method is used as follows: a galliumcompound such as gallium acetylacetonate is dissolved in an acid such ashydrochloric acid to prepare a raw-material solution; the raw-materialsolution is atomized into raw-material fine particles; the raw-materialfine particles are carried by a carrier gas onto the film formingsurface of the sample; and the raw-material fine particles being in amist state is caused to react to form a thin film on the film formingsurface. Thus, a gallium oxide-based thin film having high crystallinityis formed on the sample.

To form a semiconductor device using a gallium oxide-based thin film, itis required to control the electrical conductivity of the thin film.Patent Literature 1 and Non-Patent Literature 1 [Electrical ConductiveCorundum-Structured α-Ga₂O₃ Thin Films on Sapphire with Tin-Doping Grownby Spray-Assisted Mist Chemical Vapor Deposition, Japanese Journal ofApplied Physics, 51 (2012) 070203] disclose technologies for doping anα-gallium oxide thin film.

SUMMARY OF INVENTION

The methods of Patent Literature 1 and Non-Patent Literature 1 allow aformation of a highly conductive α-gallium oxide thin film. However,when the present inventors further examined these methods, they foundthat while about 300 nm-thick α-gallium oxide thin films formed usingthese methods were highly conductive immediately after these thin filmswere formed, the resistances thereof increased after the thin films wereheated at 500° C. and thus the semiconductor properties and the electronconductivity thereof were lost. A typical semiconductor devicemanufacturing process includes a step in which films are formed and afollowing step in which the films are heated at 500° C. or more.Accordingly, increases in the resistance of the films by heating at suchtemperatures are a serious problem.

Typically, the control of the conductivity of a semiconductor materialis focused on controlling the dopant concentration and improving theactivation rate of the activation annealing subsequent to doping. Basedon this principle, the inventors doped an α-gallium oxide thin filmusing methods disclosed in Patent Literature 1 and known documents andthen heated the semiconductor in order to perform the activationannealing and the ohmic annealing. As a result, they faced a resistanceincrease (2 to 4 digit resistance value) problem.

A typical cause of the above resistance increase problem is that, whenthe contamination elements are heated, they move within the crystal andstay in positions in which they block the movement of electrons. Fromthis viewpoint, the inventors took measures for eliminating thecontamination elements. Further, in order to find an optimum annealingcondition under which an electrically inactive state is achieved evenwhen a trace amount of contamination element remained, the inventorstook various measures, including the reduction of the annealingtemperature, the optimization of the annealing profile, and the controlof the annealing atmosphere. However, the resistance increase problemwas not solved.

Taking the above-mentioned problems into consideration, the objective ofthe present invention is to provide a highly conductive crystallinemultilayer structure including a corundum-structured crystalline oxidethin film whose resistance has not increased even after annealing(heating).

In order to achieve the above-mentioned objective, the present inventorshave made intensive investigation. As the result, they found that when a1 μm or more-thick corundum-structured crystalline oxide thin film wasannealed, the electrical resistivity did not increase but ratherdecreased. The present inventors conducted further examination and thenfinally completed the present invention.

According to the present invention, a crystalline multilayer structureincludes a base substrate and a corundum-structured crystalline oxidethin film disposed directly on the base substrate or with another layertherebetween. A thickness of the crystalline oxide thin film is 1 μm ormore, and an electrical resistivity thereof is 80 mΩcm or less.

In the crystalline multilayer structure of the present invention, thecorundum-structured crystalline oxide thin film has not increased in theresistance even after annealing and therefore is highly conductive.Accordingly, the crystalline multilayer structure is useful forsemiconductor devices and the like.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows an example configuration of a crystalline multilayerstructure of an embodiment of the present invention;

FIG. 2 is a configuration diagram of a mist CVD apparatus used inExample of the present invention; and

FIG. 3 is a graph showing the relationship between the thickness of acrystalline oxide thin film and the resistance value according toExample of the present invention.

FIG. 4 is a TEM image in Test Example.

FIG. 5 is a TEM image in Test Example.

DESCRIPTION OF EMBODIMENTS

A crystalline multilayer structure of an embodiment of the presentinvention includes a base substrate and a corundum-structuredcrystalline oxide thin film disposed directly on the base substrate orwith another layer therebetween. The thickness of the crystalline oxidethin film is 1 μm or more and the electrical resistivity thereof is 80mΩcm or less. As used herein, the “crystalline multilayer structure”refers to a structure including one or more crystal layers and mayinclude layers other than the crystal layers (e.g., amorphous layers).Each crystal layer is preferably a monocrystalline layer, but may be apolycrystalline layer. The crystalline oxide thin film may be one whichhas been annealed after being formed. Further, due to the oxidation ofan ohmic electrode by annealing, a metal oxide film may be formedbetween the crystalline thin film and the ohmic electrode. Examples ofthe ohmic electrode include indium and titanium.

Base Substrate

The base substrate is not particularly limited as long as it serves as abase for the crystalline oxide thin film, but is preferably acorundum-structured substrate. Examples of a corundum-structuredsubstrate include sapphire substrates (e.g., c-plane sapphiresubstrates) and α-phase gallium oxide substrates. The base substrateneeds not necessarily have a corundum structure. Examples of a basesubstrate not having a corundum structure include substrates having ahexagonal structure (e.g., 6H—SiC substrates, ZnO substrates, GaNsubstrates). For a substrate having a hexagonal structure, it ispreferred to form a crystalline oxide thin film directly on the basesubstrate or with another layer (e.g., buffer layer) therebetween. Thethickness of the base substrate is not particularly limited, but ispreferably 50 to 2000 μm, more preferably 200 to 800 μm.

Crystalline Oxide Thin Film

The crystalline oxide thin film is not particularly limited as long asit is a corundum-structured crystalline oxide film. But it preferablyincludes a corundum-structured oxide semiconductor as a major component,since the semiconductor properties are improved. The crystalline oxidethin film also preferably includes a non-magnetic metal (e.g., Ga, Ti,V, In) as a major component rather than a magnetic metal (e.g., Fe, Co,Ni), since the semiconductor properties are improved. The crystallineoxide thin film is preferably monocrystalline, but may bepolycrystalline. For the composition of the crystalline oxide thin film,preferably, the atomic ratio of the sum of gallium, indium, aluminum andiron to all the metal elements included in the thin film is 0.5 or more;more preferably, the atomic ratio of gallium to all the metal elementsis 0.5 or more. The preferable atomic ratio is, for example, 0.5, 0.6,0.7, 0.8, 0.9, or 1 and may be between any two of the values presented.Use of such a preferable atomic ratio allows the electrical resistivityto be more favorably reduced by annealing. If the atomic ratio ofgallium to all the metal elements is 0.5 or more and the thickness ofthe corundum structured crystalline oxide thin film is less than 1 μm,the thin film significantly increases in resistance when annealed. Incontrast, if the atomic ratio of gallium to all the metal elements is0.5 or more and a thickness of the crystalline oxide thin film is 1 μmor more, the thin film significantly decreases in the electricalresistivity when annealed. In this case, the electrical resistivity ofthe crystalline oxide thin film is reduced to 80 mΩcm or less, while itis reduced preferably to 50 mΩcm or less, more preferably to 25 mΩcm orless.

The composition of the crystalline oxide thin film is preferably, forexample, In_(X)Al_(Y)Ga_(Z)Fe_(V)O₃ (0≤X≤2.5, 0≤Y≤2.5, 0≤Z≤2.5, 0≤V≤2.5,X+Y+Z+V=1.5 to 2.5), more preferably 1≤Z. In this formula, preferable X,Y, Z, and V are each 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2,2.3, 2.4, or 2.5. Preferable X+Y+Z+V is, for example, 1.5, 1.6, 1.7,1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, or 2.5. X, Y, Z, and V and X+Y+Z+V mayeach be between any two of the values presented. Note that theabove-mentioned formula represents the composition of atoms on latticepoints forming a corundum structure. As is apparent from the fact thatthe formula is not described in the form of “X+Y+Z+V=2”, the formula mayinclude a non-stoichiometric oxide, which then may include ametal-deficient oxide or an oxygen-deficient oxide.

The crystalline oxide thin film is formed directly on the base substrateor with another layer therebetween. Examples of the said another layerinclude corundum-structured crystal thin films having anothercomposition, not-corundum-structured crystal thin films, and amorphousthin films.

The crystalline oxide thin film may be doped at least partially (morespecifically, partially in the thickness direction). It may also have amonolayer structure or a multilayer structure. If the crystalline oxidethin film has the multilayer structure, it is formed by laminating thinfilms, for example, an insulating thin film and a conductive thin film.However, the present invention is not limited thereto. If thecrystalline oxide thin film has the multilayer structure in which theinsulating thin film and the conductive thin film are laminated, thecompositions of these thin films may be the same or different. Thethickness ratio of the conductive thin film to the insulating thin filmis not particularly limited, but is preferably, for example, 0.001 to100, more preferably 0.1 to 5. This more preferable ratio is, forexample, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3,1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, or 5, or may be between any twoof the values presented.

The conductivity of the conductive thin film may be obtained by doping.The concentration of doping impurities is determined as appropriatebased on properties of the conductive thin film is required to have andis, for example, 1E15/cm³ to 1E20/cm³. The type of the doping impuritiesis not particularly limited, but includes, for example, dopantcontaining at least one selected from Ge, Sn, Si, Ti, Zr, and Hf. Theinsulating thin film usually need not be doped, but may be doped to theextent that it does not exhibit conductivity.

The thickness of the crystalline oxide thin film in the presentembodiment is 1 μm or more. Typically, a crystalline oxide thin film isformed with the thickness of about 300 nm. When a crystalline oxide thinfilm having such the thickness is heated, the resistance of theconductive thin film thereof is increased. This problem has not beensolved anyhow. In the present embodiment, on the other hand, acrystalline oxide thin film is formed with the thickness of 1 μm ormore. When this crystalline oxide thin film is heated, an increase inthe resistance of the conductive thin film thereof is prevented. Theupper limit of the thickness of the crystalline oxide thin film is notparticularly limited, but is preferably 100 μm, more preferably 50 μm,most preferably 20 μm. The most preferable thickness of the crystallineoxide thin film is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, or 20 μm, or may be between any two of thevalues presented. By setting such the thickness, the electricalresistivity can be more favorably reduced by annealing.

The crystalline multilayer structure of the present embodiment ismanufactured by generating raw-material fine particles by atomizing araw-material solution, carrying the raw-material fine particles into afilm-forming chamber using a carrier gas, forming a corundum-structuredcrystalline oxide thin film having the thickness of 1 μm or more fromthe raw-material fine particles on the base substrate in thefilm-forming chamber, and then annealing the corundum-structuredcrystalline oxide thin film. Thus, the electrical resistivity of thecrystalline oxide thin film is reduced to 80 mΩcm or less by theannealing.

A method of forming the crystalline oxide thin film is not particularlylimited, but, for example, the crystalline oxide thin film can be formedby mixing a gallium compound, an indium compound, an aluminum compound,and an iron compound according to the composition of the crystallineoxide thin film and then oxidizing the resulting raw-material compound.Thus, a crystalline oxide thin film can be grown on the base substratefrom the base substrate side. The gallium and indium compounds may beobtained by serving gallium metal and indium metal as start materialsand converting them into the gallium and indium compounds immediatelybefore forming a film. The gallium, indium, aluminum, and iron compoundsare, for example, organometallic complexes (e.g., acetylacetonatecomplexes) or halides (fluorides, chlorides, bromides, or iodides) withrespect to the respective metals. The dopant raw materials are, forexample, metals or metal compounds (e.g., halides, oxides) serving asdoping impurities. In order to form a thick film stably, it is possibleto prevent an increase in surface roughness by introducing Br or I intothe thick film. Conceivable dopants for controlling electronconductivity include, but not limited to, n-type dopants such as Ge, Sn,Si, Ti, Zr, or Hf. By introducing an n-type dopant which is ten or moretimes higher in concentration than Br or I, which serves as an abnormalgrain inhibitor, the carrier density is easily controlled. Br or I,which serves as the abnormal grain inhibitor, may also be used as ann-type dopant to control electron conductivity.

By using such an abnormal grain inhibitor, it is possible to reduce thesurface roughness (Ra) of the crystalline oxide thin film to 0.1 μm orless to further improve the semiconductor properties. As used herein,the surface roughness (Ra) refers to an arithmetic average roughnessvalue obtained by making a measurement according to JIS B0601.

The x-ray half-width of the crystalline oxide thin film is not limitedto a specific half-width. In particular, the x-ray half-width need notnecessarily be improved, but when the crystalline oxide thin film isformed with the thickness of less than 1 μm. That is, even when thex-ray half-width of the crystalline oxide thin film is not improved, theresistance can be reduced by annealing.

More specifically, the crystalline oxide thin film can be formed byatomizing the raw-material solution having the raw-material compoundsdissolved therein, generating the raw-material fine particles from theraw-material solution, carrying the raw-material fine particles into thefilm-forming chamber, and causing the raw-material compounds to react inthe chamber. The solvent of the raw-material solution is preferablywater, hydrogen peroxide water, or organic solvent. In order to form adoped thin film, the raw-material compounds may be oxidized in thepresence of dopant raw-materials. The dopant raw materials arepreferably added to the raw-material solution and then atomized with theraw-material compounds.

Note that according to the above process, the crystalline oxide thinfilm can be formed with the thickness of 1 μm or more by adjusting thefilm-forming time.

In the present embodiment, the electrical resistivity can be reduced to80 mΩcm or less by annealing. The electrical resistivity (mΩcm) ismeasured using a four-point probe measurement device according to thefour-point probe method (JIS H 0602: testing method of resistivity forsilicon crystals and silicon wafers with four-point probe). Theannealing temperature is not particularly limited as long as theelectrical resistivity can be reduced to 80 mΩcm or less, but ispreferably 600° C. or less, more preferably 550° C. or less, mostpreferably 500° C. or less. By annealing the crystalline oxide thin filmat such the preferable temperature, the electrical resistivity can bereduced more favorably. The annealing time is not particularly limitedas long as the objects of the present invention are not impaired, but ispreferably 10 seconds to 10 hours, more preferably 10 seconds to onehour.

Example Configuration of Crystalline Multilayer Structure

FIG. 1 shows a preferred example of the crystalline multilayer structureof the present embodiment and a semiconductor device using thecrystalline multilayer structure. In an example of FIG. 1, a crystallineoxide thin film 3 is formed on a base substrate 1. The crystalline oxidethin film 3 is formed by laminating an insulating thin film 3 a and aconductive thin film 3 b in this order from the base substrate side. Agate insulating film 5 is formed on the conductive thin film 3 b. A gateelectrode 7 is formed on the gate insulating film 5. Source/drainelectrodes 9 are formed on the conductive thin film 3 b so as tosandwich the gate electrode 7. Such a configuration allows for a controlof a depletion layer formed in the conductive thin film 3 b by anapplication of a gate voltage to the gate electrode 7, thereby allowingfor a transistor operation (FET device).

Examples of a semiconductor device formed using the crystallinemultilayer structure of the present embodiment include transistors orTFTs such as MIS or HEMT, Schottky barrier diodes using ametal-semiconductor junction, p-n or PIN diodes combined with anotherp-type layer, and light emitting/receiving devices.

Example

Described below is an Example of the present invention. While a dopedcrystalline oxide thin film is formed by the mist CVD in the Examplebelow, the present invention is not limited to this Example.

1. CVD Apparatus

First, referring to FIG. 2, a CVD apparatus 19 used in this Example willbe described. The CVD apparatus 19 includes a sample stage 21 forplacing a sample 20 on which films are to be formed, such as a basesubstrate, a carrier-gas source 22 for providing a carrier gas, a flowrate control valve 23 for controlling the flow rate of the carrier gassent from the carrier-gas source 22, a mist source 24 including araw-material solution 24 a, a container 25 containing water 25 a, anultrasonic transducer 26 attached to the bottom of the container 25, afilm forming chamber 27 formed of a 40-mm-inner-diameter quartz tube,and a heater 28 disposed around the film forming chamber 27. The samplestage 21 is formed of quartz, and the surface thereof for placing thesample 20 is inclined from the horizontal plane. By forming both thefilm forming chamber 27 and the sample stage 21 from quartz, entry ofapparatus-derived impurities into the films formed on the sample 20 isreduced.

2. Preparation of Raw-Material Solution

Condition 1

An aqueous solution was prepared from gallium bromide and germaniumoxide such that the atomic ratio of germanium to gallium was 1:0.05. Tofacilitate dissolution of germanium oxide, a 48% solution of hydrobromicacid was added to the aqueous solution at a volume percent of 10%.

Condition 2

Another aqueous solution was prepared such that the molar ratio betweengallium bromide and tin bromide is 1:0.01. To facilitate dissolution, a48% solution of hydrobromic acid was added to the aqueous solution at avolume percent of 10%.

In both conditions 1 and 2, the concentration of gallium bromide was setto 1.0×10⁻² mol/L. Each raw-material solution 24 a thus prepared wasinjected into the mist source 24.

3. Preparation for Film Forming

Next, a 10 mm-side square, 600 μm-thick c-plane sapphire substrate wasplaced as the sample 20 on the sample stage 21. Then the heater 28 wasactivated to raise the temperature in the film forming chamber 27 to500° C. Next, the flow rate control valve 23 was opened to send thecarrier gas from the carrier-gas source 22 into the film forming chamber27. After the carrier gas sufficiently substituted for the atmosphere inthe film forming chamber 27, the flow rate of the carrier gas wasadjusted to 5 L/min. An oxygen gas was used as the carrier gas.

4. Formation of Thin Film

Next, the ultrasonic transducer 26 was vibrated at 2.4 MHz so that thevibration was propagated to the raw-material solution 24 a through thewater 25 a. Thus, the raw-material solution 24 a was atomized intoraw-material fine particles. The raw-material fine particles werecarried into the film forming chamber 27 by the carrier gas and then thethin film was formed by a CVD reaction on the film forming surface ofthe sample 20. The film thickness was controlled by adjusting the filmforming time.

5. Evaluation

The phases of the respective thin films formed under conditions 1 and 2were identified. The identification was made by 2θ/ω scanning each thinfilm at angles of 15 to 95 degrees using an XRD diffractometer for thinfilms. Then, measurements were made using CuKα rays. As a result, theformed thin films were found to be corundum-structured α-gallium oxidethin films.

After 0.5 mm-diameter indium electrodes were pressure-bonded on eachthin film at intervals of 1 mm, each thin film was annealed at 500° C.in a nitrogen atmosphere for 20 minutes. After annealing, XRDmeasurements were made again. It was confirmed that no phase transitionoccurred and the crystal structure of α-gallium oxide was maintained.

Note that in this Example, the thicknesses of the thin films weremeasured using an interference thickness meter.

FIG. 3 shows annealing-induced changes in the resistance of theα-gallium oxide thin films formed under condition 1. As is apparent inFIG. 3, when the up to 0.3 μm-thick α-gallium oxide thin films disclosedin Patent Literature 1 or Non-Patent Literature 1 were annealed, theresistance increased; when the 1 μm-thick α-gallium oxide thin film ofthe present embodiment was annealed, the resistance dramaticallydecreased.

Annealing-induced changes in the resistance of the α-gallium oxide thinfilms formed under condition 2 were evaluated as well. The results areshown in Table 1. As shown in Table 1, no resistance increase wasobserved in the 1 μm or more-thick α-gallium oxide thin films, whetherthe dopant is Ge or Sn.

TABLE 1 Film thickness Ge (condition 1) Sn (condition 2) 0.1 μm x x 0.3μm x x 1 μm ∘ ∘ 2 μm or more ∘ — ∘: Resistance decreased by annealing x:Resistance increased by annealing —: Not performed

Then, 0.3 and 1 μm-thick β-gallia-structured β-gallium oxide thin filmswere formed on a β-gallia-structured base substrate under the samecondition as in condition 1 and then annealed at 500° C. in a nitrogenatmosphere for 20 minutes. Then, the above α-gallium oxide thin filmswere compared with the resulting thin films. The results are shown inTable 2. While the 0.3 μm-thick β-gallia oxide thin film did notincrease in resistance, the 0.3 μm-thick α-gallium oxide thin filmincreased in resistance. This result suggests that an increase in theresistance of a conductive thin film is a problem specific to acorundum-structured crystalline oxide thin film. In Table 2, “∘”indicates that the electrical resistivity was 80 mΩcm or less.

TABLE 2 Film thickness α-gallium oxide β-gallium oxide 0.1 μm x — 0.3 μmx Δ 1 μm ∘ Δ 2 μm or more ∘ — ∘: Resistance decreased to 1.0E+5Ω or lessΔ: Resistance did not change x: Resistance increased to 1.0E+7Ω or more

Next, it was checked how the resistances of α-gallium oxide thin filmsformed under condition 1 changed depending on the annealing condition.As shown in Table 3, the 300 nm (0.3 μm)-thick thin film increased inresistance at all the annealing temperatures. In Table 3, “∘” indicatesthat the electrical resistivity was 80 mΩcm or less.

TABLE 3 Annealing temperature 0.3 μm 1 μm 400° C. Δ ∘ 500° C. x ∘ 600°C. x — ∘: 1.0E+5Ω or less Δ: 1.0E+5Ω to 1.0E+7Ω x: 1.0E+7Ω or more

Comparative Example

An α-gallium oxide thin was formed on an sapphire substrate under thesame condition as in condition 1 except that there was no annealing andthe film-forming conditions were set as shown in Table 4. The filmthickness and the specific resistance of the obtained crystallinemultilayer structure were measured. The result is shown in Table 4.

TABLE 4 Film-forming Buffer Carrier Film Specific temperature layer gasthickness resistance value 500° C. α-Ga₂O₃ Forming 8.3 μm 178 mΩcm(formed at gas 800° C.)

Test Example: TEM Image

An α-gallium oxide thin was formed on an sapphire substrate under thesame condition as in condition 1 except that the film-formingtemperature was set to 600° C. The film thickness of the obtainedcrystalline multilayer structure was measured by use of TEM. Theobtained TEM image is shown in FIG. 4. The film thickness was measuredto be 4.56 μm. A TEM image for the crystalline multilayer structureobtained in Comparative Example is shown in FIG. 5.

The crystalline multilayer structure of the present invention is usefulfor semiconductor devices, including transistors or TFTs such as MIS orHEMT, Schottky barrier diodes using a metal-semiconductor junction, p-nor PIN diodes combined with another p-type layer, and lightemitting/receiving devices.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A corundum-structuredcrystalline oxide film comprising: metal elements that comprise gallium(Ga), wherein the corundum-structured crystalline oxide film has athickness of 1 μm or more, the corundum-structured crystalline oxidefilm has a surface roughness (Ra) of 0.1 μm or less, and thecorundum-structured crystalline oxide film has an atomic ratio ofgallium (Ga) to all of the metal elements comprised in thecorundum-structured crystalline oxide film to be 0.5 or more.
 2. Thecorundum-structured crystalline oxide film of claim 1, wherein thecorundum-structured crystalline oxide film has an electrical resistivityof 80 mΩcm or less.
 3. The corundum-structured crystalline oxide film ofclaim 1, wherein the corundum-structured crystalline oxide filmcomprises a dopant.
 4. The corundum-structured crystalline oxide film ofclaim 1, wherein the dopant has a concentration that is 1E15/cm³ to1E20/cm³.
 5. The corundum-structured crystalline oxide film of claim 3,wherein the dopant comprises at least one selected from Ge, Sn, Si, Ti,Zr, and Hf.
 6. The corundum-structured crystalline oxide film of claim3, wherein the corundum-structured crystalline oxide film iselectrically conductive.
 7. A semiconductor device comprising: thecorundum-structured crystalline oxide film of claim 3; and an electrodethat is electrically connected to the corundum-structured crystallineoxide film.
 8. A corundum-structured crystalline oxide film comprising:metal elements that comprise at least one metal element selected fromamong gallium, indium, aluminum, and iron, wherein thecorundum-structured crystalline oxide film has a thickness of 1 μm ormore, the corundum-structured crystalline oxide film has a surfaceroughness (Ra) of 0.1 μm or less, the corundum-structured crystallineoxide film has an atomic ratio of a sum of at least one metal elementselected from among gallium, indium, aluminum, and iron, and the atomicratio of the sum of the at least one metal element selected from amonggallium, indium, aluminum, and iron to all of the metal elementscomprised in the corundum-structured crystalline oxide film is 0.5 ormore.
 9. The corundum-structured crystalline oxide film of claim 8,wherein the corundum-structured crystalline oxide film has an electricalresistivity of 80 mΩcm or less.
 10. The corundum-structured crystallineoxide film of claim 8, wherein the corundum-structured crystalline oxidefilm comprises a dopant.
 11. The corundum-structured crystalline oxidefilm of claim 8, wherein the corundum-structured crystalline oxide filmhas an atomic ratio of gallium (Ga) to all of the metal elementscomprised in the corundum-structured crystalline oxide film to be 0.5 ormore.
 12. The corundum-structured crystalline oxide film of claim 10,wherein the dopant comprises at least one selected from Ge, Sn, Si, Ti,Zr, and Hf.
 13. The corundum-structured crystalline oxide film of claim10, wherein the crystalline oxide film comprises a composition that isrepresented by In_(X)Al_(Y)Ga_(Z)Fe_(V)O₃ (0≤X≤2.5, 0≤Y≤2.5, 0≤Z≤2.5,0≤V≤2.5, X+Y+Z+V=1.5 to 2.5).
 14. The corundum-structured crystallineoxide film of claim 13, wherein the composition comprised in thecrystalline oxide film is 1≤Z.
 15. A semiconductor device comprising:the corundum-structured crystalline oxide film of claim 10; and anelectrode that is electrically connected to the corundum-structuredcrystalline oxide film.
 16. A corundum-structured crystalline oxide filmcomprising: metal elements that comprise at least one metal selectedfrom among gallium, indium, aluminum, and iron, wherein thecorundum-structured crystalline oxide film has a thickness of 1 μm ormore, the corundum-structured crystalline oxide film has an electricalresistivity of 80 mΩcm or less, the corundum-structured crystallineoxide film has an atomic ratio of a sum of the at least one metalelement selected from among gallium, indium, aluminum, and iron, and theatomic ratio of the sum of the at least one metal element to all of themetal elements comprised in the corundum-structured crystalline oxidefilm is 0.5 or more.
 17. The corundum-structured crystalline oxide filmof claim 16, wherein the corundum-structured crystalline oxide film hasa surface roughness (Ra) of 0.1 μm or less.
 18. The corundum-structuredcrystalline oxide film of claim 16 further comprising: a dopant thatcomprises at least one selected from Ge, Sn, Si, Ti, Zr, and Hf.
 19. Thecorundum-structured crystalline oxide film of claim 16, wherein thecorundum-structured crystalline oxide film has an atomic ratio ofgallium (Ga) to all of the metal elements comprised in thecorundum-structured crystalline oxide film to be 0.5 or more.
 20. Thecorundum-structured crystalline oxide film of claim 16, wherein thecorundum-structured crystalline oxide film is monocrystalline.
 21. Asemiconductor device comprising: the corundum-structured crystallineoxide film of claim 18; and an electrode that is electrically connectedto the corundum-structured crystalline oxide film.
 22. Thecorundum-structured crystalline oxide film of claim 16, wherein thecrystalline oxide film comprises a composition that is represented byIn_(X)Al_(Y)Ga_(Z)Fe_(V)O₃ (0≤X≤2.5, 0≤Y≤2.5, 0≤Z≤2.5, 0≤V≤2.5,X+Y+Z+V=1.5 to 2.5).
 23. The corundum-structured crystalline oxide filmof claim 22, wherein the composition comprised in the crystalline oxidefilm is 1≤Z.